Yes, I would expect so. Even the OBDI on my 22R-E can tell failures at this high level. The only point I would make is that not meeting failure criteria does not equal perfectly running either. A marginal or misadjusted actuator/sensor could still be under the fail trigger. I dinked with my AFM trying to tune my EFI to my cam by tightening and loosing the flapper spring, which tricks the ECU into varying the amount of fuel it delivers. Technically my AFM was 'failed' compared to stock setting but it wouldn't show up as a diagnosable failure because the AFM was still sending a perfectly valid signal but would have made a 100% stock engine run poorly.

Quote:

FWIW, there were two missing bolts of the four between the air cleaner housing and the hose that connects to the throttle body inlet, creating a fairly good sized leak on the clean side of the air flow. We replaced those bolts and fixed that leak.

I assumed that when the code said "open #4 injector" that it meant electrically open, therefore not energizing and opening to let fuel through.

It does, the ECU only knows electrical conditions, but they are electromechanical devices and it's not unusual at all for them to leak as the seats and seals get old. Also 'open' just means the coil impedance is out of range, so it might not have just really opened but the solenoid is just weak and only partially actuating. The only way to really know is measure it.

That can sometimes be done without taking the injectors out. Part of the troubleshooting steps to check connections and voltages at the ECU first because a broken wire would look like a failed injector to the computer and soldering is a lot cheaper than a new injector. On the 22R-E the injectors are not individually controlled but it sounds like on the Subaru they are (at least it knows one has failed). So you might be able to measure each circuit at the ECU and at the injector, which is handy. FWIW my injector coils are nominally about 14 ohms and at the ECU output should measure a minimum of 10V.